Just sitting here goofing around with things I've not really dabbled with. I attempted tile mapping for the first time this morning.

Tile sheet:

Screenshot of Test Running:
{"name":"606875","src":"\/\/djungxnpq2nug.cloudfront.net\/image\/cache\/8\/e\/8e486e77b94eae78ff1606cfc6e58799.png","w":642,"h":512,"tn":"\/\/djungxnpq2nug.cloudfront.net\/image\/cache\/8\/e\/8e486e77b94eae78ff1606cfc6e58799"}

Code for it (used ugly globals and terrible practices, but I was in a hurry so I did it sporadic) :

Just can't figure why it seems to have the grey lines across it. Not bad for a first time though.

Even have a semi-working game done too, Global Destruction. I have to tweak some of the things in the code and remove a couple of things, then I'll post the code here too.

Depressing Not because of the content, but the form. Giving yourself credit is also an art. I suck at it too I'm trying to improve that too I'm definitely getting better at it, just like you >_>
The line might also be an artefact from linear filtering sampling over the bound... maybe. Or from the new floating point screen coordinates^[1], where you should use an offset of 0.5.

Already the name's good.

p.s.

if(map[i][j] == 0)
    al_draw_bitmap(spr[0], i * BLOCK_SIZE, j * BLOCK_SIZE, 0);
if(map[i][j] == 1)
    al_draw_bitmap(spr[1], i * BLOCK_SIZE, j * BLOCK_SIZE, 0);
if(map[i][j] == 2)
    al_draw_bitmap(spr[2], i * BLOCK_SIZE, j * BLOCK_SIZE, 0);
if(map[i][j] == 3)
    al_draw_bitmap(spr[3], i * BLOCK_SIZE, j * BLOCK_SIZE, 0);

could be replaced with:

al_draw_bitmap(spr[map[i][j]], i * BLOCK_SIZE, j * BLOCK_SIZE, 0);

Your code works for me unchanged with this map

10 10
3 1 1 1 3 1 1 1 1 3
2 0 0 0 2 0 0 0 0 2
2 0 0 0 2 0 0 0 0 2
2 0 0 0 2 0 0 0 0 2
3 1 1 1 3 1 1 1 1 3
2 0 0 0 2 0 0 0 0 2
2 0 0 0 2 0 0 0 0 2
2 0 0 0 2 0 0 0 0 2
2 0 0 0 2 0 0 0 0 2
3 1 1 1 3 1 1 1 1 3

{"name":"47058783.png","src":"\/\/djungxnpq2nug.cloudfront.net\/image\/cache\/7\/a\/7ab2d353a3840d48c502494acffa37e0.png","w":640,"h":508,"tn":"\/\/djungxnpq2nug.cloudfront.net\/image\/cache\/7\/a\/7ab2d353a3840d48c502494acffa37e0"}

I was gonna post a response earlier, until I realized I didn't have a solution.

The problem is a rounding error with the nearest-neighbour texture filtering going on, combined with how Allegro offsets pixels by 0.5f by default so that the middle of each pixel is drawn. Apparently, your video card is rounding the vertical result in the wrong direction.

You MIGHT be able to solve the problem by offseting your pixels by tiny decimal amounts, like 0.0001f, but this could also affect other players. Adding in linear filtering would theoretically solve this problem too, but linear filtering in Allegro works with the scaling system so I have no idea if it will apply properly to an unscaled image, nor which mode you need to use to accomplish that, MIN or MAG.

You may wanna go through your graphics card settings instead first to see if there's any texture related options that could be to blame.

It doesn't? Where the heck did I read that then...

...or wait... that would actually make more sense to Specter's problem because his textures are starting up by 1 pixel, so if for some obscure reason it's rounding a precise value of 0 down to the next lowest pixel...

Hmm... maybe adding 0.0001f really would solve all the problems?

I'm using Gimp 2.8 to do the images and I thought it started its pixels at 0. Either way I tried doing an offset of 0.5 and 1 and it didn't fix it. Sadly my laptop is an old piece of shit and has (according to Sysinfo):

so I don't know if a new driver would help or even if they have a new driver.

Direct3D stuff is offset by 0.5 behind the scenes, but that is just to make it match OpenGL so user code is compatible. Unless you know a lot about D3D you don't even know about this.

The 0.5 thing people talk about is with some non-filled primitives like lines and rectangles. When you specify x and y of a line you're specifying the center of the line. So if you want a 1 pixel thick line, you specify the center (by adding 0.5) and 1 for thickness. But it's not always 0.5 you want. If you want a 1.5 thick line you'd specify 0.75 offsets. The lines "grow out" in both directions away from the center you give.

That screenshot looks just like it is supposed to look if something was adding 0.5 pixels offsets. Maybe try with the OpenGL driver.

Yes, don't add any offset yourself. Put this before the al_create_display:

al_set_new_display_flags(ALLEGRO_OPENGL);

Oh, you're using linux, then it already was using OpenGL.

Looks like you found a bug - we do not support interlaced .png files. I didn't even know those existed. So, just re-save tilesheet.png in Gimp without interlacing and it should work.

Two things, in sprite.cpp I added a check on num as I was getting subscript out of range errors.

And in main line 225 I had to change CENTER to CENTRE.

What number is being higher than 4? According to my test code all three numbers should be 0 to 4 (5 entries). Should have 5 colored ship sprites (0 to 4), randomly pick between those to draw each redraw. Where did I mess up at? GNU never complained about that once when I compiled and ran it.